Influence of carbon segregation to dislocations on thermal desorption spectrum of hydrogen in medium carbon martensitic steels

Abstract

A computer program was developed to simulate competitive hydrogen trapping and carbon segregation to the trap site which are often referred to site competition, and the spectra of medium carbon martensitic steels, which were analyzed previously assuming a single trap energy, were re-examined. The McNabb-Foster equations in which carbon segregation was treated as trapping to the defect site were solved simultaneously incorporating a phenomenological interaction coefficient between hydrogen and carbon within the trap site. Assuming that the primary trap site of hydrogen was dislocation, experimental TDA peaks, 50-100°C lower than those of heavily deformed pure iron, were reproduced well both in height and width with a narrow range of the interaction coefficient no matter hydrogen was charged at room temperature or high temperature, i.e. prior to martensitic transformation. Due to relatively faster segregation kinetics of carbon the peak temperature does not appear to be sensitive to the carbon content or the carbon occupancy prior to thermal desorption analysis in medium carbon steels. © 2013 ISIJ.